Redox Reactions

Definition

• Redox Reaction: A chemical process where electrons are transferred between species.
• Energetically favorable electron transfer depends on ionization energies and electron affinities.

Example Reaction: Sodium and Chlorine

• Chemical Equation: 2 Na + Cl₂ → 2 NaCl
  • Chlorine is a diatomic molecule, requiring two sodium atoms to form sodium chloride.

Half Reactions

• Oxidation Half Reaction:
  • Two sodium metal atoms lose one electron each.
  • Result: Two sodium ions and two electrons.
• Reduction Half Reaction:
  • One chlorine molecule gains two electrons (from sodium ions).
  • Result: Two chloride ions.

Terminology

• Oxidation: Involves loss of electrons.
• Reduction: Involves gain of electrons (charge is reduced).
  • Neutral chlorine gains electrons to become negatively charged chloride ions.
• Reducing Agent:
  • Sodium acts as a reducing agent.
  • Sodium is oxidized (loses electrons), aiding in reducing another substance.
• Oxidizing Agent:
  • Chlorine acts as an oxidizing agent.
  • Causes sodium to be oxidized.

Redox Reactions Without Electron Transfer

• Example: Hydrogen gas and chlorine gas forming hydrochloric acid.
• Oxidation Numbers:
  • Elements: Always zero.
  • Monoatomic Ion: Oxidation number equals its charge.
  • Hydrogen: Usually +1, but -1 when bound to metals.
  • Oxygen: Usually -2, but less if bound to itself.
  • Halogens: Usually -1.
  • Sum of oxidation numbers in a compound must equal zero, or the charge on a polyatomic ion.
• Example: In H₂S, hydrogen is +1 and sulfur is -2.

Conclusion

• Understanding of electron transfer and oxidation numbers is crucial to redox chemistry.